The present invention relates to seaming the ends of an absorbing papermaker's fabric to form an endless belt for use on papermaking equipment, specifically for seaming the ends of a wet felt as used in papermaking.
Conventionally, papermaking machines have three basic sections: the forming section, the wet press section, and the drying section. In the forming section, paper pulp, which is almost liquid, is introduced onto a permeable forming fabric. The forming fabric transports the aqueous paper pulp across suction boxes thereby forming an aqueous paper web or sheet having a concentration of approximately 20% dry matter, essentially cellulose or similar fibers.
The aqueous paper web is then transported on fabrics known as wet felts, between press rolls in the wet press section of the papermaking machinery. Such a felt generally comprises, an open-mesh base fabric having at least one batt needled thereto. The pressure of the press rolls causes the water to leave the paper web; the water runs through the interstices of the wet felts. Wet felts are designed such that marking and crushing of the aqueous paper web is avoided during the dewatering process.
The paper web exits the wet section of the papermaking equipment as a sheet of approximately 45% dry matter. Thereafter, the paper sheet is carried on fabrics, known as dryer felts, through the drying section of the papermaking equipment where more water is removed through evaporation as the paper is transported around heated rollers.
In the dryer section of the papermaking equipment, the paper sheet is more resistant to marking. Conventional techniques for seaming papermaker's fabrics for the dryer section of the papermaking machine have proven satisfactory.
In contrast with the dryer section, the aqueous paper web is much softer as it passes through the wet section of the papermaking equipment. Accordingly, the risk of marking the paper is much greater. Any variation in the thickness, composition, or surface texture of the papermaker's fabric may cause marking of the aqueous web as it passes through the press rollers.
As noted previously, a papermaker's wet felt may be comprised of a base fabric having one or more batts needled thereto. The base fabric is generally made of stiff and mechanically resistant woven yarns to withstand the tensions of the belt and to maintain a desired void volume for liquid to be extracted from the paper web during the manufacturing process. The batts are made of intermingled, generally fine and flexible fibers to form a soft surface. This permits the application of pressure to the aqueous paper web while it is transported by the wet felt through the wet section of a papermaking machine to extract liquid therefrom without marking it.
When fully installed on a papermaking machine, the wet felt is in the form of a continuous belt which transports the aqueous paper web through the papermaking equipment. Although it is possible to manufacture papermaker's fabric as an endless loop, it is not always feasible to do so because the varying requirements of different types of papermaking equipment. Furthermore, there are, as known to those skilled in the art, practical limitations on the length of a felt which may be woven endless.
Generally, in lieu of an endless woven fabric, an open or flat woven fabric of a desired length is provided to the paper mill. The ends of the fabric are seamed when the fabric is installed on the papermaking equipment to form the required continuous belt. However, seaming the fabric ends is problematic since the seam may cause marking of the paper web as it transports the web through the nip of the press rollers of the papermaking equipment. It is important that the seam in a papermaker's fabric which is employed in the wet section of a papermaking machine has the same thickness and surface texture as the remainder of the fabric so that the aqueous paper web does not become marked.
There are techniques for seaming batt-on-base papermaker's fabrics known in the art. For example, it is known in the art to configure the ends of the base fabric with intermeshing loops which may b e joined with the insertion of a pintle therethrough when the end loops are intermeshed. The thickness of the pintle which joins the base fabric ends is comparable to the thickness of the yarns which comprise the cross machine yarns of the base fabric so that the seam does not create a bulge in the fabric. The ends of the batts, which are configured to abut each other, are then secured in position to the base fabric through the application of an adhesive and/or needling along the seam of the batts.
European Patent application Publication No. 0 108 733 (Nordiskafilt AB) discloses such a method for joining the ends of a batt-on-base papermaker's wet felt. According to the teachings of that patent, the base fabric of the wet felt is first manufactured and its ends are joined together in a conventional manner, such as through the insertion of a pintle discussed above. Thereafter at least one flexible fiber batt is needled onto the entirety of at least one surface of the base fabric, a portion of the batt material covering the sam in the base fabric. The batt material is then cut across the width of the fabric parallel to and a short distance behind the seam in the base fabric. Thereafter, the portion of the batt material, extending longitudinally from the cut is loosened across the seam and lifted off the base fabric to permit removal of the joining pintle so that the ends of the fabric can be disconnected.
Through this process, a flap of bat material which extends beyond one end of the base fabric is created. The flap abuts, but does not overlap, the other end of the batt when the base fabric is seamed.
When such a felt is installed on a papermaking machine, its ends are rejoined to configure the wet felt into an endless belt. The base fabric is first seamed together through the insertion of the joining pintle. Thereafter, the flap of batt material is returned to its original position abutting the other end of the batt. The flap of batt material may be bonded in place through the use of an adhesive and/or by needling the ends of the batt to the base fabric.
In practice, the abutting ends of the batt along the seam of the batt material may intermesh slightly, on the order of approximately one half the thickness of the batt. However, the seam of the batt may exhibit some discontinuities or irregularities with respect to the paper web supporting surface of the wet felt defined by the batt.
The resultant seamed fabric disclosed in E.P.O. Publication No. 0,108,733 provides a relatively good seam for its intended purpose. However, due to the highly deformable nature of the aqueous paper web as it is transported by the wet felt, some marking of the paper web which is attributable to the seam still occurs.
The specific purpose of the present invention is to obtain a good continuity between the two ends of the batt after the junction of the base fabrics.